The use of a conventional electric hand drill to crank and start a small internal combustion engine has been proposed by a number of persons. See, for example, U.S. Pat. Nos. 2,816,535; 2,901,911; 2,932,292; 3,537,436; 3,596,647 and also 3,885,544.
But despite numerous proposals and an increasing number of small engines in use, very little, if any, apparatus for safely and conveniently coupling a drill to an engine has appeared on the market or otherwise been made available to the public.
I have invented apparatus for coupling an electric drill to the shaft of an internal combustion engine which is very inexpensive to manufacture, simple to install, and safe and reliable to use.
In addition to a hand held electric drill and the internal combustion engine to be started, my invention consists of a novel elongated nut to be screwed onto the shaft of the engine and a tool to be held in the chuck of the drill and then coupled with the nut.
The nut is preferably hexagonal in cross-section and axially bored and tapped so that the nut can be screwed onto the exposed threaded end of a shaft of the engine. One end of the nut is machined to form a pair of V-shaped slots, each slot having a first face or side parallel to the axis of the nut and the other side at an angle of about 60.degree. to the first side. The apex of the V-shaped slot is preferably rounded.
The tool chucked into the electric drill is made from a conventional flat faced bit for boring holes in wood. The sharp tip and cutting edges of the bit are filed down and rounded off to make a safe and frictionless connection between the tool and the nut mounted on the engine shaft.
To crank and start the engine, the elongated hexagonal nut is screwed onto the exposed end of the engine shaft and the tool is chucked into the electric hand drill. The tool is then inserted into the two slots in the end of the nut with the tip of the tool protruding into the hole in the nut and thus preventing the tool from slipping sideways out of coupling engagement with the nut.
The tool is pressed firmly against the nut and then turned on. As the drill shaft and tool turn, the flat faces of the tool bearing against the two sides of the slots lying parallel to the axis of the nut force the nut and engine shaft to turn at the speed of the drill, thereby cranking the engine until it starts.
The engine will then pick up speed until its speed exceeds that of the drill. As this happens, the nut will begin to turn faster than the tool, and the tool will be forced out of engagement with the nut by sliding along the 60.degree. sloped sides of the slots in the nut. This prevents any possible wrenching or violent movement of the hand held drill as it is removed from engagement with the rapidly turning engine.